1. Field
The subject invention relates to transporting of substrates for processing in a vacuum processing environment.
2. Related Art
Vacuum processing systems are used to fabricate hard-drive disks, semiconductor computer chips, solar panels, and the like, from substrates made of materials such as semiconductor wafers, glass, stainless steel, etc. Typically, the vacuum processing systems include several substrate chambers that perform various processes that modify the substrate by performing deposition, cleaning, etching, heating/cooling, etc., on the substrate The substrates are generally transported to the processing systems in cassettes holding several substrates in a clean atmospheric environment, and then the substrates are transported from the cassette, one by one, through a loadlock into the vacuum environment of the system.
FIG. 1 illustrates a prior art system that includes tracks 164 for transporting cassettes 162 containing a given number of substrates 166. The tracks 164 are maintained in a clean atmospheric environment, and leads to loading chamber 170, which is maintain in vacuum. Once cassette 162 enters the vacuum environment of loading chamber 170, a knife blade 168 removes substrates 166, one by one, from the cassette 162 and transfers them into a loading module, which loads each substrate 166 onto a single substrate carrier 156. In an alternative embodiment the carriers are double substrate carriers, in which case the loading module loads two substrates at a time. Thereafter the carrier 156 and substrate 166 are moved into elevator 160 and raised to the second level to begin traversing the plurality of processing chambers 140, each of which operating in vacuum environment and is isolated from other processing chambers during processing. The motion of the carrier 156 is shown by the arrows. Once processing is completed, the substrate 166 is removed from the carrier 156 and is placed in the cassette 162 by knife blade 168. The cassette then exists from the other side of loading chamber 170 on a second set of tracks. An example of such a system is disclosed in U.S. Pat. No. 6,919,001, which is commercially available under the trademark 200 Lean® for fabrication of, e.g., hard disk used in hard disk drives.
Another system for disk fabrication brings the cassettes into a vacuum environment. In such system, a front end module is maintained in vacuum, and a loadlock permits transporting a cassette carrying, e.g., 25 substrates into the vacuum environment. A secondary vacuum chamber may be provided, wherein a buffer station supporting the 25 substrates is stationed between two robots. The first robot transfer the 25 substrates from the cassette to the buffer station, and a second robot transfers the substrates onto carriers. The carriers may be single or double substrate carriers. As can be understood, having the cassettes travel into a vacuum environment necessitates a rather large gate valve and either a large pump or long pumping period, which slows the system. Also, since the cassette travels over tracks, particles may be generated, which may be brought into the vacuum environment when the cassette travels into the vacuum chamber. Such particles can introduce unwanted defects. Also, since the cassettes travel in atmospheric environment, the cassettes and substrates tend to absorb a lot of water vapor, which then is brought into the vacuum environment and needs to be pumped out. This is especially true for cassettes made of plastic material. Moreover, the secondary chamber housing the two robots and the buffer station must be constructed to be rather large, which requires long pumping time to maintain vacuum environment. An example of such a system is illustrated in U.S. Pat. No. 6,319,373.
FIG. 2 illustrates a prior art system wherein a front end system 260 includes provisions for supporting cassette 262 containing a plurality of substrates 266. The front end 260 maintains therein a clean atmospheric environment. A robotic arm 268 removes substrates 266, one by one, from the cassette 262 and transfers them into a loadlock 270. Mainframe system 272 maintains therein a vacuum environment and includes therein a transfer robot arm 274, operating in the vacuum environment. The robot arm 274 removes substrates 266, one by one, from loadlock 270 and transfer each substrate 266 to one of processing chambers 276a-276e. Notably, substrates 266 cannot be transferred from one of processing chambers 276 to another one, without first going through main frame 272, which drastically slows processing throughput in such architecture. Once processing is completed, the substrate 166 is removed from the processing chamber by the arm 274 and is placed in the loadlock 270, to be removed by robot arm 268 and placed in the cassette 262. Several examples of such an architecture are disclosed in U.S. Pat. No. 5,844,195, which also discloses systems transporting two wafers in tandem.
The prior art systems suffer from the problem of synchronizing transport time, vacuum pumping time, and process time. That is, when a substrate is moved from atmospheric condition into vacuum condition, a loadlock or transfer chamber is used together with a vacuum pump to evacuate the air entering the chamber during the transfer of the substrate. However, transporting the substrate and pumping the chamber into a vacuum environment may take considerable time, such that it slows the throughput of the entire system.